A STUDY  OF  THE  COMBUSTION  OF  ORGANIC  MATERIALS 

IN  CLAY 


By 


ALBRA  HENRY  FESSLER 


THESIS 


FOR  THE 


DEGREE  OF  BACHELOR  OF  SCIENCE 

IN 

CERAMIC  ENGINEERING 


COLLEGE  OF  ENGINEERING 
UNIVERSITY  OF  ILLINOIS 


1921 


Digitized  by  the  Internet  Archive 
in  2016 


https://archive.org/details/studyofcombustioOOfess 


NOV  V- 


UNIVERSITY  OF  ILLINOIS 


Juxi.e...!. 19121. 

THIS  IS  TO  CERTIFY  THAT  THE  THESIS  PREPARED  UNDER  MY  SUPERVISION  BY 
ALBRA 

ENTITLED A..  C,OOUSTI  

,111  CLAYS 

IS  APPROVED  BY  ME  AS  FULFILLING  THIS  PART  OF  THE  REQUIREMENTS  FOR  THE 
DEGREE  OF MCir^LO.B. .QE S.C.IEH.C2I 


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T/iBLE  OF  CONTENTS 


I INTRONIJCTICN 

Page 


(a)  Carbon  in  clay.... 1 

(b)  Iron  in  clay 2 

(c)  Critical  period  in  burning. 2 

( d)  Steam. . 3 


II  EXPERIMENT. ^ 

(a)  Peterminat i on  of  the  carbon  content  of  the  clay....  3 


(b(  Principle  of  the  method 5 

(c)  Apparatus  and  method 5 

(d)  Procedure 7 

(e)  The  use  of  MnO,,  as  an  oxidizing  agent 7 

III  RESULTS 

(a)  Pis  cuss  ion  of  results 9 

(b)  Summary 9 

IV  BIBLIOGRAPHY 


1.  E. Orton,  Trans.  Amer . Cer. Soc . Vol.5,  p.377  (l903) 

2.  J.W.Mellcr,  Trans .Eng . Cer. Soc . ” 16, p. 259  (l916) 

3.  A.Hcpwood  & ¥. Jackson,  Trans. Eng. Cer. Soc.  Vol.2  ,p.93 

(1901) 

4.  Scotts  Standard  Methods  of  Chemical  Analysis 

2nd . Vol . p . 105 . 


T 


IITTRODUOTIOU 


The  presence  of  organic  materials  in  clays  and 
their  importance  in  the  burning  behavior  of  clays  has  long  been  a 
knov/n  fact.  It  was  noticed  that  burning  clays  with  high  carbon 
content  presented  a very  different  problem  from  burning  clays  with 
lov/  or  medium  percentages  of  carbon.  In  some  cases  v/here  the  carbon 
was  very  high  the  kiln  would  "burn  itself"  after  a dull  rod  heat 
was  obtained.  If  the  burning  v/as  not  under  absolute  control  at  that 
point  the  kiln  would  over-burn  causing  a total  loss  of  the  contents. 

Another  peculiar  circumstance  in  burning  clay 
which  is  attributed  to  the  presence  of  carbon, is  the  presence  of  a 
black  core  in  the  interior  of  the  finished  product.  These  cores 
may  be  due  to  carbon  or  to  ferrous  iron,  or  both.  They  may  thus  be 
developed  in  clays  with  no  carbon  but  with  a high  iron  content.^ 

The  burning  of  such  clays  presents  a very  interesting  problem  and 
one  that  must  be  v/orked  out  -for  each  clay. 

(^)  _Ca_rbon  in  clay.-  Carbon  in  clays  occurs  in  a form 
closely  allied  to  bituminous  coal  or  as  partially  decayed  vegetable 
tissue,  such  as  roots  and  leaves.  This  starts  to  burn  as  the  kiln 
attains  a dull  red  heat.  The  vegetable  matter  burns  readily  and 

with  no  danger  to  the  v/are.  All  of  our  burning  troubles  are  caused 

b^  tia.e  bituminous  form  of  carbon.  This  form!  of  carbon  gives  off 

a combustible  gas  which  will  burn  on  the  surface  of  the  brick  if 

enough  is  present.  This  causes  a rise  in  temperature  which  is  not 
desired  at  this  point.  Experiments  show  that  brick  v;ith  5^  sawdust 
shov/  no  core  at  the  end  of  45  hours  burning  but  with  coal,  t}ie  core 


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(b)  Iron  in  clay.-  Iron  occurs  in  two  forms  in  clay, 

depending;  on  burning  conditions.  Ferrous  iron  forms  in  the  presence 

% 

of  carbon  v;ith  no  excess  air,  while  ferric  iron  results  from  excess 
1 

air . 

(c)  Critical  period  in  burning.-  Up  to  110°  "water 
of  plasticity"  is  driven  off.  The  v/ater  left  in  the  clay  coming 
from  the  dryer  is  usually  called  "hygroscopic  water" . From  110°  to 
500  or  600°  the  clay  substance  breaks  up  and  the  "chemical  water" 

is  driven  off . The  clay  is  nov;  at  a dull  red  heat  and  if  air  is 
circulating  the  carbon  starts  to  burn.  The  rate  of  burning  increas- 
es with  increase  in  temperature.  The  carbon  near  the  surface  burns 
first,  leaving  a dark  core  in  the  center.  As  the  air  attacks  the 
carbon  in  the  interior  of  the  brick,  the  passages  between  the 

grains  of  clav  become  choked  v;ith  CO  or  CO  and  C 0 which  must  dif- 

2 ^ 

fuse  outv/ard  before  fresh  air  can  enter  and  burn  the  carbon.  This 
process  requires  time, since  the  diffusion  of  gases  through  small 
capillaries  is  a.  slow  process.  Between  900  and  1000°  the  pores 
start  to  close  up,  so  the  passage  of  e,ir  is  restricted.  It,  is 
absolutely  necessary  to  have  complete  oxidation  before  this  contra, ct- 
ion  has  progressed  to  any  great  extent.  At  1000°  the  ferrous  iron 

fuses  in  contact  with  the  clay,  and  so  if  oxidation  is  not  complete 
a.nd  the  ferrous  iron  is  not  oxidized  to  ferric  iron  at  this  point, 
we  have  formed  a slag  v/hich  slows  up  oxidation  due  to  the  increasing 
difficult^''  of  air  entering  into  the  interior.  In  bad  cases  the 
bubbles  entangled  wath  the  fusing  slag  cause  the  brick  to  swell  and 
bloat.^ 


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(d)  Stepjn » » The  state  of  the  atmosphere  circulating 

v/hi  ch 

around  the  brick  during  oxidation  determines  the  rate  at^fresh  air 
penetrates  the  interior  of  the  vra.re . The  more  air  the  better, 
as  brick  in  badly  ventilated  parts  of  the  kiln  are  more  apt  to  have 
cores.  The  effect  of  steam  in  the  kiln  is  to  act  as  a screen 
preventing  the  entrance  of  air,  so  it  is  necessary  to  remove  all 
steam  as  quickly  as  possible. 

II  SXPERIT.CETTTAI. 

(a)  Determination  of  the  carbon  content  of  the  clay.-. 

The  clay  used  in  this  v/ork  V7as  obtained  from  the  Coates’  Manufactur- 
ing CorTipany,  Fort  Dodge,  Iowa,  and  v;as  a blaclf  shale  used  in  the 

making  of  brick  and  tile.  The  carbon  content  was  determined  by 

4 

the  " Scott  Wet  Process”  , using  the  apparatus  shown  in  Fig.Fo.l. 

One  gram  of  the  clay  was  mixed  with  10  grams  K^Cr  0 

^ 2 7 

PS  an  cxidizer  in  flask  A.  50  cc.  cf  H SO  v/as  admitted 

2 4 

through  B and  then  boiled  for  five  minutes.  Before  adding  the 

H SO  , the  system  was  cleaned  out  by  drawing  air  through  the  train 
2 4 

for  five  minutes,  and  then  v/eighing  U tubes  C and  D,  After 
oxidation  wa.s  complete  the  tv/o  U tubes  were  v^eighed  again.  The  in« 
crease  in  v/eight  showed  the  amount  of  CO  absorbed  b^^  the  Ma  Ca. 

This  amount  multiplied  by  .2727  gave  the  amount  of  carb on^  v/hich 
divided  by  the  amount  of  clay  used  a,nd  multiplied  by  100  gave  the 
percentage.  Three  preliminary  tests  were  run  and  then  three 
complete  tests,  giving  3.93,  3.S  and  9^  of  carbon. 


; 5,  *, 

MMiniBiK. 


-5- 


(b)  Principle  of  the  method.-  To  carry  on  the  study  of 

the  coinhustion  of  organic  materials  in  clay,  it  v/a.s  desired  to  find 

the  amount  of  CO  given  off  during  oxidation.  To  accomplish  this 

2 

it  was  necessary  to  find  some  way  of  measuring  this  gas.  Our 
first  attempt  v;as  with  the  use  of  gas  mete-rs.  e volume  of  gas  and 
air  v/as  measured  by  one  meter,  the  gas  then  passing  through  a CO 

2 

absorption  tra.in  and  then  through  a second  meter.  The  difference 

in  the  two  meter  readings  would  give  us  the  CO  content  of  the 

2 

gas.  This  process  was  not  successful  due  to  the  fact  that  the 
hydrocarbons  in  the  gas  tended  to  interfere  v;ith  the  accuracy  of 
the  meters.  The  apparatus  finally  adopted  is  shown  in  Pig. No. 2. 

(c)  Aonaratus  and  method.-  The  furnace  used  v/as  made  of 
a 4”  porcelain  tube  and  covered  with  an  asbestos  coverii-ig.  It  was 
wound  Y/ith  No.  20  chromel  wire,  connected  in  series  with  an  ammeter 
and  a rheostat  used  to  vai’y  the  current.  The  outer  end  of  the 
furnace  v/as  closed  with  a perforated  disk,  softer  the  sample  was  in 
place.  At  the  other  end  a porcelain  tube  connected  with  a conden- 
ser and  drip  bottle  to  collect  the  moisture  from  the  gasses.  The 

drying  of  the  gases  were  completed  by  passino-  through  a H .SO  wash 

2 4 

bottle.  The  CO,,  v/as  absorbed  by  passing  through  a solution  of 

KOH  made  by  dissolving  300  grams  cf  KOH  in  300  grams  of  v/ater. 

The  gases  a;nd  air  then  passed  through  another  drying  tube  containing 

H SO  which  collected  all  v/ater  given  up  by  the  KOK  solution. 

2 4 

This  absorption  train 

v/as  placed  on  a balance  pa.n  so  the  am.ount  of  CO  absorbed  could  be 
weighed.  The  draft  through  the  furnace  was  obtained  by  means  of 


i 


-7- 

a vacuum  pump  run  by  a smalTi  motor.  A manometer  which  had  been 
calibrated  by  means  of  a ga.s  meter  was  attached  to  the  train.  By 
reading*  the  manometer,  the  volume  of  air  passing  through  the  fur- 
nace was  known. 

(d)  Procedure.-  The  cube  of  clay  was  placed  in  the 
center  of  the  furnace  with  a thermocouple  beside  it.  Pieces  of 
brick  were  placed  in  front  of  the  cube  so  as  to  divert  the  in- 
coming air  to  all  parts  of  the  brick.  The  suction  pump  was  started 
so  as  to  produce  a draft  of  2 cubic  feet  of  air  per  minute  through 
the  furnace.  This  draft  was  kept  constant  through  all  the 

experiments.  The  air  would  burn  the  carbon  to  CO^  and  pass  through 

the  H SO  bottle  into  the  KOH  solution  where  the  CO  was  absorbed. 

2 4 2 ' 

These  bottles  were  placed  on  a balance  so  the  amount  of  CO 

2 

absorbed  in  the  KOH  solution  could  be  weighed  at  a given  time.  The 
temperature  was  kept  constant  for  each  run.  Several  tests  were 
made  at  each  temperature  and  the  results  checked.  The  results 
obtained  are  shown  graphically  in  Pig.  Ho.  3.  The  points  for  a 
given  run  are  indicated  by  the  use  of  the  same  color. 

( e)  The  use  of  MnQ^  as  an  oxidizing  agent.-  It  v/as 

desired  to  know  what  effect  MnO  v/ould  exert  unon  the  oxidation  of 

2 

the  clay.  With  this  idea  in  view  some  of  the  clay  was  ground  to 
pass  through  a 20  mesh  screen  and  cubes  of  clay  were  made  mixing 
1,  3,  5,  3 and  10"'^  of  5ln0^  v;ith  the  clay.  The  clay  was  pressed  in 
a 2"  X 2”  X 2”  mould  and  burned  in  a muffle  kiln.  Draw  trials  were 
drawn  at  500,  600,  700,  800  and  900  degrees.  Ho  decrease  in  the 
size  of  the  cores  could  be  seen,  except  in  the  ones  containing  10!^ 


76  ^m5  CO^  Q>VOlve.d. 


-9- 


MnO  • This  decrease  could  be  seen  for  each  trial  dra?/n,  showing 
2 

that  MnO  acted  as  an  oxidizer  at  all  temperatures  at  \7hich  trials 
2 

were  drawn  and  with  the  same  effect  at  all  these  temperatures. 

Ill  RESULTS 

(a)  Discussion  of  results.-  The  results  obtained  are 
rather  v/hat  one  would  expect  from  preceding  knowledge  of  the 
oxidation  process.  The  slight  difference  in  the  data  for  differ- 
ent runs  at  the  same  temperature  is  due  to  the  difference  in  texture 
of  the  samples.  The  curves  shov/  the  marked  increase  in  the  rate 
of  oxidation  for  each  increase  in  the  temperature.  is  interest- 

ing to  note  the  slight  increase  in  the  rate  of  oxidation  with  the 

addition  of  lInO  . It  would  be  interesting  to  find  the  increase 
2 

in  the  rate  of  oxidation  at  a constant  temperature,  with  varying 
volumes  of  air.  The  time  available  was  not  sufficient  to  take  up 
this  side  of  the  problem. 

("b)  Summary.  - The  results  of  the  investigation  are  shown 
on  Dig.  ho.  3. 


